Semiconductor devices, such as integrated circuits, are manufactured in batches with an intent to make the chips identical. Batch manufacturing of the chips is useful in lowering manufacturing costs. However, it is desirable to be able to distinguish an individual integrated circuit from others, for example to track its source of manufacture, or to identify a system employing the integrated circuit. Individually identifiable integrated circuits may be used to validate transactions, route messages, track items, recover stolen goods, etc. Further, many such devices which conform to certain security protocols are required to have unique identifiers. The devices may have unique encryption keys to make it difficult to hack into the devices.